1. Field of the Invention
This invention relates to a temperature distribution measuring instrument for obtaining a thermal image of an object to be measured by detecting infrared rays from the object such as a human body. More specifically, it relates to a temperature distribution measuring instrument for use in the control of a car air conditioner or the like.
2. Description of the Prior Art
The Applicant proposes a temperature distribution measuring instrument for measuring a temperature distribution of a driver or passenger by detecting infrared rays from the driver or passenger, a seat and the like in a vehicle with incident light temperature sensors (to be referred to as "infrared sensors" hereinafter) in Japanese Laid-open Patent Application No. Hei-8-101671. This instrument comprises a sensor array consisting of infrared sensors arranged linearly inside an inner cylinder, an outer cylinder having a plurality of slits in its side portion, and the inner cylinder rotating inside the outer cylinder and having a slit in its side portion. It detects infrared rays radiated from the driver and the like in the vehicle, calculates temperature data based on the outputs of the infrared sensors of the sensor array and measures a temperature distribution in the vehicle. The slit in the rotating inner cylinder has a chopper function to transmit and cut off input infrared rays and the sensor array detects infrared rays from each part of the object passing through the slits in the outer cylinder along with the rotation of the inner cylinder as one column of a matrix sequentially to obtain a 2-D thermal image of the object. This temperature distribution measuring instrument is installed on top of the dashboard or therearound, back view mirror, room lamp, pillar or the like to detect a required area in the vehicle so that a temperature distribution mainly in an upper part including the thigh and portions therearound of the body of a driver seated in a driver's seat can be measured. FIG. 6 shows an example of the temperature distribution measuring instrument 1 which is installed on a portion near the top of a dashboard 5 almost in front of a driver 4 seated in a driver's seat 3 inside a vehicle 2.
As shown in FIG. 7(a), the temperature distribution measuring instrument 1 of the prior art comprises an outer cylinder 7 having a plurality of slits 7s, an inner cylinder 8 internal to the outer cylinder 7, having a slit 8s and sharing a center axis with the outer cylinder 7, a lens 9 for converging infrared rays radiated from the driver 4, driver's seat 3 and the like in the vehicle and input into the temperature distribution measuring instrument 1 through a slit 7s in the outer cylinder 7 and the slit 8s in the inner cylinder 8, a sensor array 10 for detecting the above input infrared rays, and inner cylinder drive means 11 for rotating the inner cylinder 8. The sensor array 10 is disposed at the center of the inner cylinder 8 and consists of a plurality of infrared sensors 10a arranged in parallel to the center axis of these cylinders as shown in FIG. 7(b).
FIGS. 8(a) and 8(b) are perspective views of the outer cylinder 7 and the inner cylinder 8, respectively. Out of infrared rays input from 16 slits 7s (701 to 716) in the outer cylinder 7, only infrared rays which are aligned with the slit 8s in the rotating inner cylinder 8 are input into the infrared sensor array 10. That is, when the inner cylinder 8 rotates clockwise as shown in FIG. 8(b), infrared rays passing through slit 701, slit 702, . . . and slit 716 in the outer cylinder 7 sequentially are input into the infrared sensor array 10 through the slit 8s in the inner cylinder 8 only for a time (input time) during which the slit 8s in the inner cylinder 8 is overlapped with the slit 7s in the outer cylinder 7. While the slit 8s in the inner cylinder 8 moves between slits 7s in the outer cylinder 7, infrared rays are cut off and not input into the infrared sensor array 10. Therefore, a thermal image measured by the temperature distribution measuring instrument 1 is obtained as a matrix consisting of a number of rows corresponding to the number of infrared sensors 10a (A to H) of the infrared sensor array 10 and a number of columns corresponding to the number of slits 7s in the outer cylinder 7, as shown in FIG. 9. In the figure, black columns between adjacent columns of the matrix indicate areas where temperature data are not obtained because infrared rays from the object 6 are cut off.
However, since the width L of each of the slits 7s in the outer cylinder 7 and the interval K between the slits 7s are fixed in the above prior art, as shown in FIG. 10, when the width W1 (to be referred to as "measurement width" hereinafter) of the object 6 radiating infrared rays to be input into the slits 7s in the outer cylinder 7 from the object 6 located in front of the temperature distribution measuring instrument 1 is L, the measurement width W2 of the object 6 through a slit which is located at an angle .alpha. from a plane passing the center axis of the cylinders and being perpendicular to the object 6 and which is in a portion away from the front side of the temperature distribution measuring instrument 1 is larger than L. Thus, W2 differs from W1. The product of the above measurement width and the length of each of the slits 7s in the outer cylinder 7 is called "measurement area" (to be exact, the area of the object radiating infrared rays to be input into the slit 8s in the inner cylinder 8). That is, temperature data on columns (1 to 8 and 9 to 16) of a thermal image are based on infrared rays input from different measurement areas. By changing the width of each column of a thermal image to a width proportional to the above measurement area, a thermal image can be expressed such that measurement areas farther from the center of the thermal image become larger, as shown in FIG. 11. Since the temperature data are essentially obtained from the quantity of radiated infrared rays per unit area, the measurement area of each column of the thermal image is larger as the angle from the above plane increases in the temperature distribution measuring instrument, thereby degrading measurement accuracy. As described above, as non-detected portions corresponding to the times during which the slit 8s in the inner cylinder 8 is shut are produced in the thermal image of the prior art, a continuous thermal image cannot be obtained.